Static electricity
Introduced| English | Meaning |
|---|---|
| static electricity/ˈstætɪk ɪlekˈtrɪsɪti/ | static electricity |
| charge/tʃɑːdʒ/ | An electrical property that causes attraction or repulsion. |
| electrons/ɪˈlektrɒnz/ | Negatively charged subatomic particles found outside atomic nuclei. |
| coulombs/ˈkuːlɒmz/ | The SI unit of electric charge, equal to the charge transferred by a current of one ampere in one second. |
| conductor/kənˈdʌktə/ | A material through which electric charge or thermal energy can pass readily. |
| insulator/ˈɪnsjuːleɪtə/ | A material in which electric charge does not move readily under ordinary conditions. |
| electric field/ɪˈlektrɪk fiːld/ | A region in which an electric charge experiences an electric force. |
| ion/ˈaɪɒn/ | An atom or group of atoms with a net electric charge from losing or gaining electrons. |
Sparks and sticky balloons
- Rub a balloon on your hair and it sticks to the wall; lightning is the same effect, in giant form.
- Both come from static electricity 静电 — charge 电荷 that has built up and is not moving.
- It all comes down to tiny electrons 电子.
Electric charge
- There are two kinds of charge: positive and negative.
- The rule is like magnetic poles: same charges repel, different charges attract.
- Charge is measured in coulombs 库仑 (C).
Rub a balloon and watch it charge
Rubbing moves electrons onto the balloon, making it negative — then it attracts a neutral wall or your hair, but repels another negative balloon.
Two negative charges attract each other.
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Like charges repel; only different charges (+ and −) attract.
Charging by friction
- Rub two different materials together and electrons (tiny negative particles) move from one to the other.
- The material that gains electrons becomes negative; the one that loses them becomes positive.
- Only the negative electrons move — the positive charge stays put.
- Example: a plastic rod rubbed with a cloth becomes negative (it gained electrons); the cloth is left positive.
When you rub a plastic rod with a cloth, the rod gains electrons. The rod becomes:
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Gaining electrons (which are negative) makes the rod negative. The cloth, having lost electrons, is left positive.
During charging by friction, what actually moves between the materials?
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Only the negative electrons move. The positive charge stays fixed in place.
Match each static-electricity idea to what it means.
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Each item links the term to its correct meaning.
Conductors 导体 and insulators 绝缘体
- A conductor (copper and other metals) lets charge flow easily, because it has free electrons.
- An insulator (plastic, rubber, glass) does not — its electrons cannot move freely.
- Test it: put the material in a circuit with a lamp and a battery — the lamp lights only for a conductor.
Why is copper a good conductor of electricity?
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A conductor has free electrons that can flow through it. Insulators have no free-moving charges.
Electric fields 电场 and ions 离子
- An electric field is a region where a charge feels a force.
- Its direction at a point is the direction of the force on a positive charge.
- Field patterns: lines point away from + and toward −; between parallel plates the lines are straight and evenly spaced.
- An atom that loses electrons becomes a positive ion; one that gains electrons becomes a negative ion.
The direction of an electric field at a point is the direction of the force on:
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By convention, the electric field direction is the direction of the force on a positive charge.
A neutral atom loses two electrons. It becomes:
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Losing negative electrons leaves more positive charge, so the atom becomes a positive ion.
You've got it
- two charges: + and −; same repel, different attract
- charging by friction moves electrons only: gain → negative, lose → positive
- conductors have free electrons; insulators do not
- electric field direction = force on a positive charge; lose electrons → positive ion